Epstein Barr virus nuclear protein 2 (EBNA-2) is essential for B cell transformation by the virus. The goal of this project is to determine the function of EBNA-2 in transformation. Since EBNA-2 is known to transactivate expression of Epstein-Barr virus and B cell genes, we determined whether EBNA-2 could directly activate transcription in vitro. Plasmids containing the DNA binding domain of GAL4 fused to portions of the EBNA-2 gene were cotransfected with a reporter plasmid in B lymphoma cells. A 37 amino acid domain of EBNA-2 activated transcription nearly as strongly as the activating domain of herpes simplex VP16. This domain is essential for B cell transformation by the virus. A 14 amino acid peptide had about 25% of the activity of the larger domain. At present, we are trying to determine (1) what cellular proteins interact with the transcriptional activation domain of EBNA-2, (2) what additional domains of EBNA-2 may interact with cellular proteins to bind viral DNA, and (3) whether other transcriptional activators can substitute for the transforming function of EBNA-2. Additional experiments have been initiated to study the ability of primary B cells transformed by EBV mutants to cause tumors in SCID mice.